Method for transmitting and receiving downlink control information in wireless communication system and device therefor

ABSTRACT

Disclosed is a method for allowing a terminal to receive a downlink signal from a base station in a wireless communication system. More specifically, the method comprises the steps of: receiving a first control channel which indicates the location information of a resource allocated to a second control channel; receiving the second control channel, on the basis of a control format indicator contained in the first control channel; and obtaining a downlink grant and/or an uplink grant contained in the second control channel, wherein the second control channel is allocated with the resource contained in a data region of a specific subframe.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for transmitting andreceiving downlink control information in a wireless communicationsystem.

BACKGROUND ART

A brief description will be given of a 3^(rd) Generation PartnershipProject Long Term Evolution (3GPP LTE) system as an example of awireless communication system to which the present invention can beapplied.

FIG. 1 illustrates a configuration of an Evolved Universal MobileTelecommunications System (E-UMTS) network as an exemplary wirelesscommunication system. The E-UMTS system is an evolution of the legacyUMTS system and the 3GPP is working on standardization of E-UMTS. E-UMTSis also called an LTE system. For details of the technicalspecifications of UMTS and E-UMTS, refer to “3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network”Release 7 and Release 8, respectively.

Referring to FIG. 1, the E-UMTS system includes a User Equipment (UE),an evolved Node B (eNode B or eNB), and an Access Gateway (AG) which islocated at an end of an Evolved UMTS Terrestrial Radio Access Network(E-UTRAN) and connected to an external network. The eNB may transmitmultiple data streams simultaneously, for broadcast service, multicastservice, and/or unicast service.

A single eNB manages one or more cells. A cell is set to operate in oneof the bandwidths of 1.25, 2.5, 5, 10, 15 and 20 Mhz and providesDownlink (DL) or Uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be configured so as to providedifferent bandwidths. An eNB controls data transmission and reception toand from a plurality of UEs. Regarding DL data, the eNB notifies aparticular UE of a time-frequency area in which the DL data is supposedto be transmitted, a coding scheme, a data size, Hybrid Automatic RepeatreQuest (HARQ) information, etc. by transmitting DL schedulinginformation to the UE. Regarding UL data, the eNB notifies a particularUE of a time-frequency area in which the UE can transmit data, a codingscheme, a data size, HARQ information, etc. by transmitting ULscheduling information to the UE. An interface for transmitting usertraffic or control traffic may be defined between eNBs. A Core Network(CN) may include an AG and a network node for user registration of UEs.The AG manages the mobility of UEs on a Tracking Area (TA) basis. A TAincludes a plurality of cells.

While the development stage of wireless communication technology hasreached LTE based on Wideband Code Division Multiple Access (WCDMA), thedemands and expectations of users and service providers are increasing.Considering that other radio access technologies are under development,new technological evolutions are required to achieve futurecompetitiveness. Specifically, cost reduction per bit, increased serviceavailability, flexible use of frequency bands, a simplified structure,an open interface, appropriate power consumption of UEs, etc. arerequired.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the conventionalproblem is to provide a method and apparatus for transmitting downlinkcontrol information in a wireless communication system.

Technical Solution

In an aspect of the present invention, a method for receiving a downlinksignal in a specific subframe from a base station at a user equipment ina wireless communication system includes receiving a first controlchannel indicating position information about resources allocated to asecond control channel, receiving the second control channel based on acontrol format indicator included in the first control channel, andacquiring at least one of a downlink grant and an uplink grant from thesecond control channel. The second control channel is allocated toresources included in a data region of the specific subframe.

The method may further include receiving a third control channelindicating whether the second control channel is transmitted.

In another aspect of the present invention, a user equipment in awireless communication system includes a reception module for receivinga downlink signal in a specific subframe from a base station, and aprocessor for processing the downlink signal. The reception modulereceives a first control channel indicating position information aboutresources allocated to a second control channel and receives the secondcontrol channel based on a control format indicator included in thefirst control channel, and the controller acquires at least one of adownlink grant and an uplink grant from the second control channel. Thesecond control channel is allocated to resources included in a dataregion of the specific subframe.

The reception module may further receive a third control channelindicating whether the second control channel is transmitted.

The control format indicator in the first control channel may indicatethe index of a starting symbol of the second control channel, the indexof an ending symbol of the second control channel, or the indexes ofstarting and ending symbols of the second control channel.

The second control channel may be precoded together with a data channelbased on a reference signal.

The third control channel may be a Physical Control Format IndicatorChannel (PCFICH) and whether the second control channel is transmittedmay be indicated by a specific state indicated by a control formatindicator of the PCFICH.

Advantageous Effects

According to the embodiments of the present invention, a base stationcan transmit downlink control information effectively, while avoidinginter-cell interference in a wireless communication system.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved with the present invention are not limited to whathas been particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a configuration of an Evolved Universal MobileTelecommunications System (E-UMTS) network as an example of a wirelesscommunication system;

FIG. 2 illustrates a control-plane protocol stack and a user-planeprotocol stack in a radio interface protocol architecture conforming toa 3^(rd) Generation Partnership Project (3GPP) radio access networkstandard between a User Equipment (UE) and an Evolved UMTS TerrestrialRadio Access Network (E-UTRAN);

FIG. 3 illustrates physical channels and a general signal transmissionmethod using the physical channels in a 3GPP system;

FIG. 4 illustrates a structure of a radio frame in a Long Term Evolution(LTE) system;

FIG. 5 illustrates a structure of a downlink radio frame in the LTEsystem;

FIG. 6 illustrates a configuration of a relay backhaul link and a relayaccess link in a wireless communication system;

FIG. 7 illustrates an example of relay node resource partitioning;

FIG. 8 illustrates the concept of carrier aggregation;

FIGS. 9, 10 and 11 illustrate exemplary methods for signaling positioninformation about an Enhanced Physical Downlink Control Channel(E-PDCCH) according to embodiments of the present invention;

FIG. 12 illustrates exemplary transmission of an Enhanced Physical HARQIndicator Channel (E-PHICH) according to another embodiment of thepresent invention;

FIG. 13 illustrates exemplary transmission of an E-PDCCH according to anembodiment of the present invention;

FIG. 14 illustrates exemplary transmission of an E-PDCCH and an E-PHICHaccording to an embodiment of the present invention; and

FIG. 15 is a block diagram of a communication apparatus according to anembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The configuration, operation, and other features of the presentinvention will readily be understood with embodiments of the presentinvention described with reference to the attached drawings. Embodimentsof the present invention as set forth herein are examples in which thetechnical features of the present invention are applied to a 3^(rd)Generation Partnership Project (3GPP) system.

While embodiments of the present invention are described in the contextof Long Term Evolution (LTE) and LTE-Advanced (LTE-A) systems, they arepurely exemplary. Therefore, the embodiments of the present inventionare applicable to any other communication system as long as the abovedefinitions are valid for the communication system.

FIG. 2 illustrates control-plane and user-plane protocol stacks in aradio interface protocol architecture conforming to a 3GPP wirelessaccess network standard between a User Equipment (UE) and an EvolvedUMTS Terrestrial Radio Access Network (E-UTRAN). The control plane is apath in which the UE and the E-UTRAN transmit control messages to managecalls, and the user plane is a path in which data generated from anapplication layer, for example, voice data or Internet packet data istransmitted.

A PHYsical (PHY) layer at Layer 1 (L1) provides information transferservice to its higher layer, a Medium Access Control (MAC) layer. ThePHY layer is connected to the MAC layer via transport channels. Thetransport channels deliver data between the MAC layer and the PHY layer.Data is transmitted on physical channels between the PHY layers of atransmitter and a receiver. The physical channels use time and frequencyas radio resources. Specifically, the physical channels are modulated inOrthogonal Frequency Division Multiple Access (OFDMA) for downlink andin Single Carrier Frequency Division Multiple Access (SC-FDMA) foruplink.

The MAC layer at Layer 2 (L2) provides service to its higher layer, aRadio Link Control (RLC) layer via logical channels. The RLC layer at L2supports reliable data transmission. RLC functionality may beimplemented in a function block of the MAC layer. A Packet DataConvergence Protocol (PDCP) layer at L2 performs header compression toreduce the amount of unnecessary control information and thusefficiently transmit Internet Protocol (IP) packets such as IP version 4(IPv4) or IP version 6 (IPv6) packets via an air interface having anarrow bandwidth.

A Radio Resource Control (RRC) layer at the lowest part of Layer 3 (orL3) is defined only on the control plane. The RRC layer controls logicalchannels, transport channels, and physical channels in relation toconfiguration, reconfiguration, and release of Radio Bearers (RBs). AnRB refers to a service provided at L2, for data transmission between theUE and the E-UTRAN. For this purpose, the RRC layers of the UE and theE-UTRAN exchange RRC messages with each other. If an RRC connection isestablished between the UE and the E-UTRAN, the UE is in RRC Connectedmode and otherwise, the UE is in RRC Idle mode. A Non-Access Stratum(NAS) layer above the RRC layer performs functions including sessionmanagement and mobility management.

A cell covered by an eNB is set to one of the bandwidths of 1.25, 2.5,5, 10, 15, and 20 MHz and provides downlink or uplink transmissionservice in the bandwidth to a plurality of UEs. Different cells may beset to provide different bandwidths.

Downlink transport channels used to deliver data from the E-UTRAN to UEsinclude a Broadcast Channel (BCH) carrying system information, a PagingChannel (PCH) carrying a paging message, and a Shared Channel (SCH)carrying user traffic or a control message. Downlink multicast trafficor control messages or downlink broadcast traffic or control messagesmay be transmitted on a downlink SCH or a separately defined downlinkMulticast Channel (MCH). Uplink transport channels used to deliver datafrom a UE to the E-UTRAN include a Random Access Channel (RACH) carryingan initial control message and an uplink SCH carrying user traffic or acontrol message. Logical channels that are defined above transportchannels and mapped to the transport channels include a BroadcastControl Channel (BCCH), a Paging Control Channel (PCCH), a CommonControl Channel (CCCH), a Multicast Control Channel (MCCH), a MulticastTraffic Channel (MTCH), etc.

FIG. 3 illustrates physical channels and a general method fortransmitting signals on the physical channels in the 3GPP system.

Referring to FIG. 3, when a UE is powered on or enters a new cell, theUE performs initial cell search (S301). The initial cell search involvesacquisition of synchronization to an eNB. Specifically, the UEsynchronizes its timing to the eNB and acquires a cell Identifier (ID)and other information by receiving a Primary Synchronization Channel(P-SCH) and a Secondary Synchronization Channel (S-SCH) from the eNB.Then the UE may acquire information broadcast in the cell by receiving aPhysical Broadcast Channel (PBCH) from the eNB. During the initial cellsearch, the UE may monitor a downlink channel state by receiving aDownLink Reference Signal (DL RS).

After the initial cell search, the UE may acquire detailed systeminformation by receiving a Physical Downlink Control Channel (PDCCH) andreceiving a Physical Downlink Shared Channel (PDSCH) based oninformation included in the PDCCH (S302).

If the UE initially accesses the eNB or has no radio resources forsignal transmission to the eNB, the UE may perform a random accessprocedure with the eNB (S303 to S306). In the random access procedure,the UE may transmit a predetermined sequence as a preamble on a PhysicalRandom Access Channel (PRACH) (S303 and S305) and may receive a responsemessage to the preamble on a PDCCH and a PDSCH associated with the PDCCH(S304 and S306). In case of a contention-based RACH, the UE mayadditionally perform a contention resolution procedure.

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S307) and transmit a Physical Uplink Shared Channel(PUSCH) and/or a Physical Uplink Control Channel (PUCCH) to the eNB(S308), which is a general downlink and uplink signal transmissionprocedure. Particularly, the UE receives Downlink Control Information(DCI) on a PDCCH. Herein, the DCI includes control information such asresource allocation information for the UE. Different DCI formats aredefined according to different usages of DCI.

Control information that the UE transmits to the eNB on the uplink orreceives from the eNB on the downlink includes a downlink/uplinkACKnowledgment/Negative ACKnowledgment (ACK/NACK) signal, a ChannelQuality Indicator (CQI), a Precoding Matrix Index (PMI), a RankIndicator (RI), etc. In the 3GPP LTE system, the UE may transmit controlinformation such as a CQI, a PMI, an RI, etc. on a PUSCH and/or a PUCCH.

FIG. 4 illustrates a structure of a radio frame used in the LTE system.

Referring to FIG. 4, a radio frame is 10 ms (327200×T_(s)) long anddivided into 10 equal-sized subframes. Each subframe is 1 ms long andfurther divided into two slots. Each time slot is 0.5 ms (15360×T_(s))long. Herein, T_(s) represents a sampling time and T_(s)=1/(15kHz×2048)=3.2552×10⁻⁸ (about 33 ns). A slot includes a plurality of OFDMsymbols or SC-FDMA symbols in the time domain by a plurality of ResourceBlocks (RBs) in the frequency domain. In the LTE system, one RB includes12 subcarriers by 7 (or 6) OFDM symbols. A unit time in which data istransmitted is defined as Transmission Time Interval (TTI). The TTI maybe defined as one or more subframes. The above-described radio framestructure is purely exemplary and thus the number of subframes in aradio frame, the number of slots in a subframe, or the number of OFDMsymbols in a slot may vary.

FIG. 5 illustrates an exemplary control channel included in the controlregion of a subframe in a downlink radio frame.

Referring to FIG. 5, a subframe includes 14 OFDM symbols. The first oneto three OFDM symbols of a subframe are used for a control region andthe other 13 to 11 OFDM symbols are used for a data region according toa subframe configuration. In FIG. 5, reference characters R1 to R4denote RSs or pilot signals for antenna 0 to antenna 3. RSs areallocated in a predetermined pattern in a subframe irrespective of thecontrol region and the data region. A control channel is allocated tonon-RS resources in the control region and a traffic channel is alsoallocated to non-RS resources in the data region. Control channelsallocated to the control region include a Physical Control FormatIndicator Channel (PCFICH), a Physical Hybrid-ARQ Indicator Channel(PHICH), a Physical Downlink Control Channel (PDCCH), etc.

The PCFICH is a physical control format indicator channel carryinginformation about the number of OFDM symbols used for PDCCHs in eachsubframe. The PCFICH is located in the first OFDM symbol of a subframeand configured with priority over the PHICH and the PDCCH. The PCFICH iscomposed of 4 Resource Element Groups (REGs), each REG being distributedto the control region based on a cell Identity (ID). One REG includes 4Resource Elements (REs). An RE is a minimum physical resource defined byone subcarrier by one OFDM symbol. The PCFICH indicates 1 to 3 or 2 to 4according to a bandwidth. The PCFICH is modulated in Quadrature PhaseShift Keying (QPSK).

The PHICH is a physical Hybrid-Automatic Repeat and request (HARQ)indicator channel carrying an HARQ ACK/NACK for an uplink transmission.That is, the PHICH is a channel that delivers DL ACK/NACK informationfor UL HARQ. The PHICH includes one REG and is scrambledcell-specifically. An ACK/NACK is indicated in one bit and modulated inBinary Phase Shift Keying (BPSK). The modulated ACK/NACK is spread witha Spreading Factor (SF) of 2 or 4. A plurality of PHICHs mapped to thesame resources form a PHICH group. The number of PHICHs multiplexed intoa PHICH group is determined according to the number of spreading codes.A PHICH (group) is repeated three times to obtain a diversity gain inthe frequency domain and/or the time domain.

The PDCCH is a physical downlink control channel allocated to the firstn OFDM symbols of a subframe. Herein, n is 1 or a larger integerindicated by the PCFICH. The PDCCH is composed of one or more CCEs. ThePDCCH carries resource allocation information about transport channels,PCH and DL-SCH, an uplink scheduling grant, and HARQ information to eachUE or UE group. The PCH and the DL-SCH are transmitted on a PDSCH.Therefore, an eNB and a UE transmit and receive data usually on thePDSCH, except for specific control information or specific service data.

Information indicating one or more UEs to receive PDSCH data andinformation indicating how the UEs are supposed to receive and decodethe PDSCH data are delivered on a PDCCH. For example, on the assumptionthat the Cyclic Redundancy Check (CRC) of a specific PDCCH is masked byRadio Network Temporary Identity (RNTI) “A” and information about datatransmitted in radio resources (e.g. at a frequency position) “B” basedon transport format information (e.g. a transport block size, amodulation scheme, coding information, etc.) “C” is transmitted in aspecific subframe, a UE within a cell monitors a PDCCH using its RNTIinformation. If one or more UEs have RNTI “A”, these UEs receive thePDCCH and receive a PDSCH indicated by “B” and “C” based on informationof the received PDCCH.

Meanwhile, when the channel state between an eNB and a UE is poor, aRelay Node (RN) is installed between them to provide a better radiochannel to the UE. In addition, use of an RN at a cell area where achannel from an eNB is in poor state can provide a high-speed datachannel and extend cell service coverage. RNs have been introduced toeliminate shadowing areas and are widely deployed in a wirelesscommunication system.

Conventionally, relaying was confined to the function of a repeater thatsimply amplifies a signal and forwards the amplified signal. However,more intelligent relay schemes have recently been developed.Furthermore, relaying is a requisite technology to reduce eNBinstallation cost and backhaul maintenance cost, while extending servicecoverage and increasing data throughput in a future-generation mobilecommunication system. Along with the growth of relaying techniques,there exists a need to support an RN used in a conventional wirelesscommunication system for a new wireless communication system.

In a 3GPP LTE-A system, with the introduction of a function of relayinga signal on a link between an eNB and a UE to an RN, two links havingdifferent attributes apply to each of DL and UL carrier frequency bands.A link between the eNB and the RN is defined as a backhaul link. Abackhaul link through which a signal is transmitted using downlinkresources in Frequency Division Duplex (FDD) or Time Division Duplex(TDD) is called a backhaul downlink, whereas a link through which asignal is transmitted using uplink resources in FDD or TDD is called abackhaul uplink.

FIG. 6 illustrates a configuration of a relay backhaul link and a relayaccess link in a wireless communication system.

Referring to FIG. 6, with the introduction of a function of relaying asignal on a link between an eNB and a UE to an RN, two links havingdifferent attributes apply to each of downlink and uplink carrierfrequency bands. A link between the eNB and the RN is defined as abackhaul link. A backhaul link through which a signal is transmittedusing downlink resources in FDD or TDD is called a backhaul downlink,whereas a link through which a signal is transmitted using uplinkresources in FDD or TDD is called a backhaul uplink.

Meanwhile, a link between an RN and a UE is defined as a relay accesslink. A relay access link through which a signal is transmitted in adownlink frequency band (in case of FDD) or in downlink subframeresources (in case of TDD) is called an access downlink, whereas a relayaccess link through which a signal is transmitted in an uplink frequencyband (in case of FDD) or in uplink subframe resources (in case of TDD)is called an access uplink.

An RN may receive information from an eNB through a relay backhauldownlink and transmit information to the eNB through a relay backhauluplink. In addition, the RN may transmit information to a UE through arelay access downlink and receive information from the UE through arelay access uplink.

With respect to an RN's usage of a frequency band (or spectrum), itsoperation can be classified into in-band and out-band. For an in-bandRN, a backhaul link shares the same frequency band with an access link.If the backhaul link and the access link operate in different frequencybands, the RN is an out-band RN. In both in-band and out-band relaying,a UE (legacy UE) operating in the conventional LTE system (e.g.Release-8) should be able to access a donor cell.

Depending on whether a UE is aware of the existence of an RN, RNs may beclassified into a transparent RN and a non-transparent RN. If the UEdoes not perceive whether it communicates with a network via an RN, theRN is a transparent RN. In contrast, if the UE perceives whether itcommunicates with a network via an RN, the RN is a non-transparent RN.

In relation to control of RNs, RNs may be classified into an RNconfigured as a part of a donor cell and an RN that self-controls acell.

The former RN may have an RN ID, although it does not have its own cellID. If at least a part of Radio Resource Management (RRM) of an RN iscontrolled by an eNB covering the donor cell, the RN is regarded asconfigured as a part of the donor cell (even though the other parts ofthe RRM reside in the RN). Preferably, this RN can support legacy UEs(e.g. LTE UEs). For instance, smart repeaters, decode-and-forwardrelays, various types of L2 RNs, and type-2 RNs form a part of a donorcell.

The latter RN controls one or more cells. The cells are allocated theirunique physical cell IDs and they may use the same RRM mechanism. Fromthe viewpoint of a UE, there is no distinction between accessing a cellcontrolled by an RN and accessing a cell controlled by a macro eNB.Preferably, a cell controlled by this type of RN may support legacy UEs.For example, RNs of this type include self-backhauling RNs, L3 RNs,type-1 RNs, and type-1a RNs.

A type-1 RN is an in-band RN that controls a plurality of cells. Each ofthe plurality of cells appears to a UE as a separate cell distinct froma donor cell. The plurality of cells have their own physical cell IDs(as defined in LTE Release-8) and the RN can transmit its ownsynchronization channels, RSs, etc. During a single-cell operation, a UEmay receive scheduling information and an HARQ feedback directly fromthe RN and transmit its control channels (a Scheduling Request (SR), aCQI, an ACK/NACK, etc.) to the RN. The type-1 RN appears as a legacy eNB(operating in conformance to LTE Release-8) to a legacy UE (conformingto LTE Release-8). That is, the type-1 RN has backward compatibility. Onthe other hand, to LTE-A UEs, the type-1 RN appears different from alegacy eNB. Thus the type-1 RN can enhance performance.

Except for its out-band operation, a type-1a RN is characterized by thesame set of features as the type-1 RN. The type-1a RN may be configuredsuch that the influence of its operation on an L1 operation is minimizedor eliminated.

A type-2 RN is an in-band RN that does not have its own physical cell IDand thus does not form a new cell. Since the type-2 RN is transparent tolegacy UEs, the legacy UEs do not notice the existence of the type-2 RN.The type-2 RN can transmit a PDCCH but does not transmit at least aCommon RS (CRS) and a PDCCH.

In order to allow in-band relaying, some resources in the time-frequencydomain should be set aside for a backhaul link and these resources maybe set not to be used for an access link. This is called resourcepartitioning.

A description will be given of the general principle of resourcepartitioning at an RN. A backhaul downlink and an access downlink may beTDM-multiplexed in one carrier frequency (that is, only one of thebackhaul downlink and the access downlink is activated at a specifictime). Similarly, a backhaul uplink and an access uplink may beTDM-multiplexed in one carrier frequency (that is, only one of thebackhaul uplink and the access uplink is activated at a specific time).

Multiplexing of backhaul links in FDD is performed such that backhauldownlink transmission and backhaul uplink transmission take place in adownlink frequency band and an uplink frequency band, respectively. Incomparison, multiplexing of backhaul links in TDD is performed such thatbackhaul downlink transmission and backhaul uplink transmission takeplace in a downlink subframe between an eNB and an RN and an uplinksubframe between the eNB and the RN, respectively.

In case of an in-band RN, for example, if backhaul downlink receptionfrom an eNB and access downlink transmission to a UE are performedsimultaneously in the same frequency band, a signal transmitted from thetransmitter of the RN may be received at the receiver of the RN. As aresult, signal interference or Radio Frequency (RF) jamming may occur atthe RF front-end of the RN. Likewise, if access uplink reception from aUE and backhaul uplink transmission to an eNB take place simultaneouslyin the same frequency band, the RF front-end of the RN may experiencesignal interference. Therefore, simultaneous eNB-to-RN and RN-to-UEtransmissions in the same frequency band may not be feasible unless areception signal and a transmission signal are sufficiently isolatedfrom each other (e.g. a Transmission (Tx) antenna is geographicallyapart enough from a Reception (Rx) antenna (e.g. installed on theground/underground)).

One way to handle the signal interference is to operate the RN such thatwhile the RN is receiving a signal from a donor cell, it is nottransmitting signals to UEs. That is, a gap is created in the RN-to-UEtransmission and UEs (including legacy UEs) are not supposed to expectany RN transmission during the gap. This gap may be created byconfiguring a Multicast Broadcast Single Frequency Network (MBSFN)subframe.

FIG. 7 illustrates an example of RN resource partitioning.

In FIG. 10, a first subframe is a general subframe in which an RNtransmits a downlink (i.e. an access downlink) control signal and datato a UE and a second subframe is an MBSFN subframe in which the RNtransmits a control signal to a UE in the control region of a DLsubframe but no transmission occurs from the RN to a UE in the otherregion of the DL subframe. Since a legacy UE expects PDCCH transmissionin every DL subframe (in other words, the RN needs to allow legacy UEswithin its area to receive a PDCCH in each subframe and thus support ameasurement function), it is necessary to transmit a PDCCH in every DLsubframe to ensure reliable operations of legacy UEs. Therefore, the RNneeds access downlink transmission in the first N (N=1, 2 or 3) OFDMsymbols of even a subframe (a second subframe 1020) configured fordownlink (i.e. backhaul downlink) transmission from an eNB to the RN,instead of backhaul downlink reception. Since the RN transmits a PDCCHto UEs in the control region of the second subframe, backwardcompatibility may be provided to legacy UEs served by the RN. The RN mayreceive a signal from the eNB in the remaining region of the secondsubframe in which no transmission occurs from the RN to UEs. Thus, anin-band RN does not perform access downlink transmission and backhauldownlink reception simultaneously by the above-described resourcepartitioning.

The second subframe using an MBSFN subframe will be described in detail.The control region of the second subframe may be referred to as an RNnon-hearing period. An RN transmits an access downlink signal withoutreceiving a backhaul downlink signal in the RN non-hearing period. TheRN non-hearing period may have 1, 2 or 3 OFDM symbols. The RN maytransmit an access downlink signal to a UE in the RN non-hearing periodand receive a backhaul downlink signal from an eNB in the other period.Since the RN cannot perform transmission and reception simultaneously inthe same frequency band, time is taken for the RN to switch from Tx modeto Rx mode. Therefore, a Guard Time (GT) needs to be set in a startingpart of the backhaul downlink reception area, for Tx/Rx mode switchingof the RN. Similarly, when the RN receives a backhaul downlink signalfrom the eNB and transmits an access downlink signal to a UE, a GT maybe set for Rx/Tx mode switching of the RN. The length of a GT may be atime-domain value, for example, k (k>1) time samples (T_(s)) or one ormore OFDM symbols. Or when RN backhaul downlink subframes aresuccessively configured or according to a predetermined subframe timingalignment relationship, a GT may not be defined or set at the end of asubframe. To maintain backward compatibility, a GT may be defined onlyin a frequency area set for backhaul downlink subframe transmission (ifa GT is set in an access downlink period, legacy UEs cannot besupported). The RN may receive a PDCCH and a PDSCH from the eNB in thebackhaul downlink reception period except for the GT. The PDCCH andPDSCH may be called an R-PDCCH and an R-PDSCH to indicate that they areRN dedicated physical channels.

It is expected that the future-generation mobile communication standard,LTE-A will support Coordinated Multi-Point (CoMP) transmission, comparedto the legacy standard, in order to increase data rate. CoMP refers totransmission of data to a UE through cooperation from two or more eNBsor cells in order to increase communication performance between a UElocated in a shadowing area and an eNB (a cell or sector).

CoMP transmission schemes may be classified into CoMP-Joint Processing(CoMP-JP) called cooperative MIMO characterized by data sharing, andCoMP-Coordinated Scheduling/Beamforming (CoMP-CS/CB).

In downlink CoMP-JP, a UE may instantaneously receive datasimultaneously from eNBs that perform CoMP transmission and combine thereceived signals, thereby increasing reception performance (JointTransmission (JT)). In addition, one of the eNBs participating in theCoMP transmission may transmit data to the UE at a specific time point(Dynamic Point Selection (DPS)). In contrast, in downlink CoMP-CS/CB, aUE may receive data instantaneously from one eNB, that is, a serving eNBby beamforming.

In uplink CoMP-JP, eNBs may receive a PUSCH signal from a UE at the sametime (Joint Reception (JR)). In contrast, in uplink CoMP-CS/CB, only oneeNB receives a PUSCH. Herein, cooperative cells (or eNBs) may make adecision as to whether to use CoMP-CS/CB.

Now, carrier aggregation will be described below. FIG. 8 illustrates theconcept of carrier aggregation.

Carrier aggregation refers to aggregation of a plurality of frequencyblocks or cells (in the logical sense of the term) including uplinkresources (or UL Component Carriers (CCs)) and/or downlink resources (orDL CCs) into one broad logical frequency band at a UE in order to a usebroader frequency band in a wireless communication system. For clarityof description, the term CC will be used uniformly.

Referring to FIG. 8, a total system band is a logical band having abandwidth of up to 100 MHz. The system band includes five CCs, each CChaving a bandwidth of up to 20 MHz. A CC includes one or more contiguousphysical subcarriers. While each CC is shown as having the samebandwidth in FIG. 8 by way of example, each CC may have a differentbandwidth. In addition, while the CCs are shown as adjacent to eachother in the frequency domain, this configuration is logical. Therefore,the CCs may be contiguous or non-contiguous physically.

Each CC may have a different center frequency or physically adjacent CCsmay have a common center frequency. For example, if all CCs arephysically contiguous, they may commonly have center frequency A. On theother hand, if the CCs are not contiguous physically, the CCs may havedifferent center frequencies A, B, etc.

In the disclosure, a CC may correspond to the system band of a legacysystem. Backward compatibility and system design may be facilitated in awireless communication environment in which evolved UEs coexist withlegacy UEs, by defining a CC from the perspective of the legacy system.For example, when the LTE-A system supports carrier aggregation, each CCmay correspond to the system band of the LTE system. In this case, a CCmay have one of the bandwidths, 1.25, 2.5, 5, 10, and 20 MHz.

When a total system band is extended by carrier aggregation, a frequencyband used for communication with a UE is defined in units of a CC. Atotal system bandwidth, 100 MHz may be available to UE A and thus UE Amay communicate using five CCs. Only 20 MHz may be available to each ofUEs B₁ to B₅ and thus each of UEs B₁ to B₅ may use one CC, forcommunication. Each of UEs C₁ and C₂ may use 40 MHz and thus maycommunicate in two CCs. The two CCs may or may not be contiguouslogically/physically. In the illustrated case of FIG. 8, UE C₁ uses twonon-contiguous CCs, whereas UE C₂ uses two contiguous CCs.

The LTE system uses one DL CC and one UL CC, whereas the LTE-A systemmay use a plurality of CCs as illustrated in FIG. 8. A data channel maybe scheduled by a control channel by conventional linked carrierscheduling or cross carrier scheduling.

In linked carrier scheduling, a control channel transmitted in aspecific CC schedules only a data channel of the specific CC, as in thelegacy LTE system using a single CC.

In cross carrier scheduling, a control channel transmitted in a primaryCC schedules a data channel transmitted in the primary CC or any otherCC by means of a Carrier Indicator Field (CIF).

Meanwhile, many techniques have been discussed in order to cancelinter-cell interference in a wireless mobile communication network inwhich a plurality of types of cells coexist. Particularly, if cells areof different types, mutual interference becomes serious. For example,interference between a macro cell (hereinafter, referred to as cell A)and a small-size, low-power cell such as a picocell or a femtocell(hereinafter, referred to as cell B) causes a more serious problem thaninterference between macro cells. For example, when cell B communicateswith a UE of cell B during communication between cell A and a UE of cellA, the UE of cell B may receive strong interference from cell A.

In the 3GPP LTE system, a downlink subframe usually carries a PDCCH anda PDSCH. If cell A and cell B belong to the same LTE system, cell A andcell B use the same subframe configuration. If cell A and cell Btransmit signals in different subframes, downlink transmission from cellA may not interfere with downlink transmission from cell B. That is,cell A and cell B use limited subframe resources in time division.However, this scheme reduces resource use efficiency significantly.Accordingly, a scheme in which the two cells share the same subframe bydividing frequency resources or spatial resources is better. Or the twoschemes may be efficiently used in combination.

Another method of reducing inter-cell interference is that a datachannel of cell A is divided spatially and steered in a differentdirection so that interference with cell B is minimized. That is, atransmission beam is steered in a corresponding direction of a specificUE by applying precoding to cell A, thus avoiding interference. As aconsequence, the influence of the data channel from cell A on a datachannel from cell B can be reduced remarkably.

However, a control channel is generally transmitted across a totalsystem band and decoded using a Common Reference Signal (CRS). If thecontrol channel is precoded, a receiver needs information about theprecoding to detect and decode the control channel. Since the precodinginformation is also delivered on a control channel, the receiver cannotdecode the control channel eventually. Accordingly, to make thisoperation viable, an additional RS is required to decode a controlchannel successfully, which may increase transmission and receptioncomplexity.

Another method of avoiding inter-cell interference is to decode acontrol channel such as a PCFICH or a PHICH using a CRS as doneconventionally for a PDCCH. However, different methods should apply todifferent control channel types. For example, it may be regulated that aPDCCH is transmitted at a specific position of a PDSCH resource regionand a PCFICH and a PHICH are transmitted in the first symbol or up tothe fourth symbols.

It may also be contemplated that the PCFICH, PHICH, and CRS are locatedin the first OFDM symbol and the PDCCH is transmitted after the thirdsymbol. Obviously, a UL grant or a DL grant transmitted on the PDCCH mayreside in the second slot as well as in the first slot. Or the DL grantmay be located only in the first slot, while the UL grant may be locatedonly in the second slot. It is assumed herein that broadcast importantsystem information, that is, a BCH, a PCH, an SCH, etc. are transmittedin the conventional manner.

A new control channel distinguished from the existing PDCCH is referredto as an Enhanced PDCCH (or E-PDCCH). When needed, the E-PDCCH may beprecoded and decoded using a dedicated RS such as a DM-RS. In addition,interference with a corresponding subframe of cell B may be minimized byapplying the same precoding to the E-PDCCH and the PDSCH, when needed.Although control information such as a PCFICH positioned in the firstsymbol may still cause more or less interference, interference from themain interference factors, PDCCH and PDSCH may be reduced considerablyby beamforming. Furthermore, since the PCFICH is subject to inter-cellhopping based on a Cell ID, it is quite robust against inter-cellinterference.

Methods for designing an E-PDCCH and an E-PHICH and a UE operation usingthe same will be described below based on the above-described concept.

Embodiment 1

A UE may determine the number of symbols used for a PDCCH from a CFIincluded in a PCFICH. [Table 1] below lists codewords corresponding toCFI values defined by the present LTE standard. Particularly, a statecorresponding to a CFI value of 4 is reserved.

TABLE 1 CFI CFI code word <b₀, b₁, . . . , b₃₁> 1 <0, 1, 1, 0, 1, 1, 0,1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0,1> 2 <1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,0, 1, 1, 0, 1, 1, 0, 1, 1, 0> 3 <1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1,1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1> 4 <0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, (Reserved) 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0, 0>

An Enhanced PCFICH or E-PCFICH of the present invention may indicate thestarting symbols of an E-PDCCH and a PDSCH as well as the number ofPDCCH symbols. In this case, the starting position of the E-PDCCH or thePDSCH may be changed according to the number of PDCCH symbols.

Specifically, if an eNB transmits the E-PCFICH in the first symbol of asubframe and starts to transmit the E-PDCCH or PDSCH in a k^(th) symbol,a UE may determine the value of k from the E-PCFICH and receive theE-PDCCH and the PDSCH at the determined position. That is, the CFI ofthe E-PCFICH may indicate the starting position k of the E-PDCCH or thePDSCH.

In addition, the E-PCFICH may indicate the frequency-domain position ofthe E-PDCCH as well as the time-domain position of the E-PDCCH. If onlythe E-PDCCH exists without any PDCCH, the E-PCFICH may be translateddifferently and serve a new usage.

While the CFI values of the PCFICH are still interpreted in theconventional manner, the reserved state may be used for various usages.If CFI=4, this may indicate that the E-PDCCH is used without any PDCCH.That is, this value may implicitly indicate the existence of only a UEusing the E-PDCCH in the corresponding subframe.

The E-PDCCH may be located at a fixed position and the position of theE-PDCCH may be changed by RRC signaling. Preferably, an initial E-PDCCHposition is set so that an E-PDCCH may be decoded successfully duringinitial access. Or the position of the E-PDCCH may be changed in asubframe carrying a PDCCH. Likewise, the position of the E-PDCCH may beindicated or changed more freely by additional RRC signaling.

Or if the eNB signals a CFI value indicating the reserved state in thePCFICH, that is, CFI=4, the UE may interpret the CFI value of 4 astransmission of an E-PDCCH and thus operation relying only on theE-PDCCH or as transmission of both a PDCCH and an E-PDCCH and decodingof the PDCCH and the E-PDCCH. Or the two interpretation methods may beset or changed by additional RRC signaling.

If the reserved state is set in a general subframe, an E-PDCCH ismeaningless to a legacy UE in the frame and thus the legacy UE is likelyto have a problem in its operation. To avert the problem, the eNB doesnot schedule the legacy UE.

A case corresponding to one of the two interpretations will be describedin detail.

1) If the CFI set to 4 indicates use of an E-PDCCH only, it is preferredto configure the E-PDCCH to be used only in a specific subframe such asan MBSFN subframe. That is, the E-PDCCH is limited to a subframeconfigured for an LTE-A UE, not an LTE UE. The LTE-A UE acquires a ULgrant and a DL grant only from the E-PDCCH.

2) If the CFI set to 4 indicates use of both a PDCCH and an E-PDCCH, itis preferred to receive a BCH, a PCH, etc. in a common search space of aPDCCH region, while receiving a UL grant and a DL grant in a dedicatedsearch space of an E-PDCCH region.

If the E-PDCCH is available only in a specific subframe such as an MBSFNsubframe, the specific subframe is preferably configured only for LTE-AUEs. Particularly, one or two symbols are allocated to a PDCCH region inthe MBSFN subframe.

If the eNB schedules only LTE-A UEs, excluding LTE UEs, the PCFICH maybe designed to be interpreted in a different manner from theconventional manner. For example, all states indicated by CFI values inthe PCFICH may be used to indicate PDCCH and E-PDCCH regions and the useor non-use of a PDCCH and an E-PDCCH.

For example, among the four states listed in [Table 1], a CFI value of“1” may indicate one PDCCH symbol and non-use of an E-PDCCH, a CFI valueof “2” may indicate two PDCCH symbols and non-use of an E-PDCCH, a CFIvalue of “3” may indicate use of both a PDCCH and an E-PDCCH and thenumber of PDCCH symbols limited to 1 or 2, and a CFI value of “4” mayindicate use of an E-PDCCH only.

Meanwhile, if CFI=4 indicating a reserved state as in 1) and 2), thenumber of PDCCH symbols needs to be assumed. In this case, regarding aPDCCH region, it may be assumed that K=0, 1, 2, . . . irrespective ofactual transmission of a PDCCH. Even though a PDCCH is not transmitted,if K=1, symbol index #0 is not used for an E-PDCCH or a PDSCH. Rather,the E-PDCCH or PDSCH may start in symbol index #1. The value of K may befixed or changed by RRC signaling.

TABLE 2 Non-MBSFN subframes Subframes 1 and 8 MBSFN subframes PHICH incase of frame All other on a carrier duration structure type 2 casessupporting PDSCH Normal 1 1 1 Extended 2 3 2

TABLE 3 Number of Number of OFDM symbols OFDM symbols for PDCCH forPDCCH Subframe when N_(RB) ^(DL) > 10 when N_(RB) ^(DL) ≦ 10 Subframe 1and 6 for frame 1, 2 2 structure type 2 MBSFN subframes on a carrier 1,2 2 supporting PDSCH. configured with 1 or 2 cell-specific antenna portsMBSFN subframes on a carrier 2 2 supporting PDSCH. configured with 4cell-specific antenna ports Subframes on a carrier not 0 0 supportingPDSCH Non-MBSFN suframes (except 1, 2, 3 2, 3 subframe 6 for framestructure type 2) configured with positioning reference signals Allother cases 1, 2, 3 2, 3, 4

[Table 2] lists PHICH durations, that is, numbers of symbols availablefor a PHICH, and [Table 3] lists numbers of PDCCH symbols according tobandwidths and subframe types.

As illustrated in [Table 2] and [Table 3], a PHICH duration may beassociated with K. That is, the value of K may be set to be equal to aPHICH duration in a subframe. Then a UE may determine the ending time ofa PDCCH without additional signaling. For example, if the PHICH durationof an MBSFN subframe is normal (“1”), K may be 1 and if the PHICHduration of an MBSFN subframe is extended (“2”), K may be 2. However, inthe case of the normal PHICH duration, the PDCCH may be longer than thePHICH. Then the number of symbols for a PDCCH region may be indicated byRRC signaling.

However, if the extended PHICH duration is set for a non-MBSFN subframe,the PDCCH may occupy up to 3 OFDM symbols. Therefore, a CFI value may bemapped to a PHICH duration so that an LTE-A UE may determine from theduration of the PHICH that the CFI is 3. Obviously, this method isintroduced to set the starting symbol of the E-PDCCH. From theperspective of interpretation, the CFI is 3, which has nothing to dowith an actual transmission region.

Meanwhile, a higher-layer parameter “pdsch-Start” is defined to signalthe starting position of a PDSCH in the LTE-A standard using carrieraggregation. The position of the starting symbol of an E-PDCCH may besignaled by the parameter. For example, if cross carrier scheduling isused without carrier aggregation, “pdsch-Start” may be transmitted andthus may be used as information indicating the position of the startingsymbol of an E-PDCCH.

FIGS. 9, 10 and 11 illustrate exemplary methods for signaling positioninformation about an E-PDCCH according to embodiments of the presentinvention.

FIG. 9 illustrates a case where a CFI of 4 in a PCFICH indicates theexistence of an E-PDCCH only, without any PDCCH in a subframe.

FIG. 10 illustrates a case where the symbol positions and frequencypositions of an E-PDCCH are indicated by an E-PCFICH. In this case, itis preferred that no legacy UE exists in a corresponding subframe.

Or the E-PCFICH may indicate the total number of symbols occupied by theE-PDCCH. It is assumed herein that the starting or ending symbol of theE-PDCCH is fixed or preset by RRC signaling.

Finally, FIG. 11 illustrates a case where an E-PDCCH resides in thesecond slot. In this case, the E-PCFICH may indicate the index of thelast symbol of the E-PDCCH in the second slot or the number of OFDMsymbols for the E-PDCCH in the second slot. In this case, it is assumedthat the E-PDCCH is designed to be steered in a specific directiontogether with a PDSCH by beamforming, rather than the E-PDCCH istransmitted across a total frequency band.

As described before, the E-PCFICH functions as the conventional PCFICHand only LTE-A UEs may demodulate and decode the E-PCFICH. Thus, thenumber and positions of OFDM symbols mapped to the E-PDCCH arepreferably limited to a specific value and specific position(s). Forexample, when a normal CP is used, the last one to three symbols of thefirst slot are allocated to the E-PDCCH.

Or the E-PDCCH may be fixed in a specific symbol. For example, if theE-PCFICH is 0, the E-PDCCH is configured to start in the second symbol,if the E-PCFICH is 1, the E-PDCCH is configured to start in the thirdsymbol, if the E-PCFICH is 2, the E-PDCCH is configured to start in thefourth symbol, and if the E-PCFICH is 3, the E-PDCCH is configured tostart in the fifth symbol.

[Table 4] below lists the indexes of starting symbols for an E-PDCCHaccording to values of an E-PCFICH in the first slot.

TABLE 4 E-PCFICH 0 1 2 3 Starting symbol of E-PDCCH 1 2 3 4 for 1^(st)slot (#1) Starting symbol of E-PDCCH 2 3 4 5 for 1^(st) slot (#2)Starting symbol of E-PDCCH 3 4 5 6 for 1^(st) slot (#3) Starting symbolof E-PDCCH 4 5 6 — for 1^(st) slot (#4) Starting syrmbol of E-PDCCH 5 6— — for 1^(st) slot (#5) Starting symbol of E-PDCCH 6 — — — for 1^(st)slot (#6)

TABLE 5 E-PCFICH 0 1 2 3 Ending symbol of E-PDCCH 0 1 2 3 for 2^(nd)slot (#1) Ending symbol of E-PDCCH 1 2 3 5 for 2^(nd) slot (#2) Endingsymbol of E-PDCCH 2 3 4 5 for 2^(nd) slot (#3) Ending symbol of E-PDCCH3 4 5 6 for 2^(nd) slot (#4) Ending symbol of E-PDCCH 4 5 6 — for 2^(nd)slot (#5) Ending symbol of E-PDCCH 5 6 — — for 2^(nd) slot (#6) Endingsymbol of E-PDCCH 6 — — — for 2^(nd) slot (#7)

If a DL grant and a UL grant are delivered in the first and secondslots, respectively and the E-PDCCH is designed to have a variablenumber of symbols, it may occur that the starting and ending symbols ofthe two grants should be indicated by one E-PCFICH. In this case, thestarting symbol of the DL grant may be limited to two positions and theending symbol of the UL grant may be limited to two positions so thatfour CFI values may indicate the starting and ending positions of the DLand UL grants, respectively. It is also possible to increase the numberof signaling cases by increasing the number of E-PDCCH states.

[Table 6] and [Table 7] illustrate examples of indicating both thestarting and ending symbol indexes of an E-PDCCH by an E-PCFICH value.Specifically, [Table 6] illustrates a case where the starting symbolindex of the E-PDCCH is 2 or 3 and [Table 7] illustrates a case wherethe starting symbol index of the E-PDCCH is 1 or 2.

TABLE 6 Ending symbol of 2^(nd) slot PDCCH (e.g. UL grant) PCFICH value(state) 6 7 Starting symbol of 1^(st) slot PDCCH 2 0 1 (e.g. DL grant) 32 3

TABLE 7 Ending symbol of 2^(nd) slot PDCCH (e.g. UL grant) PCFICH value(state) 6 7 Starting symbol of 1^(st) slot PDCCH 1 0 1 (e.g. DL grant) 22 3

Embodiment 2

An E-PHICH will be described according to another embodiment of thepresent invention. FIG. 12 illustrates an example of transmitting anE-PHICH according to another embodiment of the present invention.

1) Compared to the conventional PHICH, the E-PHICH may require anadditional RS, for demodulation and may be transmitted in theconventional PDSCH region, like an E-PDCCH and an R-PDCCH. Designing theE-PHICH based on the conventional CRS may minimize the constraint ofusing an additional RS at the expense of degradation of channelestimation performance. With the conventional CRS, a PHICH may bepositioned in the second slot.

E-PHICH resources are related to the number of allocated PUSCHresources. In addition, an E-PHICH for a specific UE is related to a UEID, a subframe index, etc.

The E-PHICH resources are indicated by higher-layer signaling. Thehigher-layer signaling may be expressed as a bitmap or as ResourceAllocation Type 0, 1 and 2 of the LTE system. The position of theE-PHICH in the determined resources may be indicated to each UE byhigher-layer signaling or may be determined based on the index of anuplink scheduled resource.

Accordingly, the UE may receive its E-PHICH based on the higher-layersignaling and the index of the uplink scheduled resource. To reflect achange in a channel, it is preferred to allocate different E-PHICHresources at different time points.

The same precoding as used for an E-PDCCH and an R-PDSCH may apply tothe E-PHICH and thus a beam may be formed for the E-PHICH such thatinterference with other cells is reduced.

2) The E-PHICH may be transmitted in a preset RB (e.g. at both ends of afrequency band). In this case, precoding for beamforming is not appliedto the E-PHICH, which may cause inter-cell interference. Since aninterfered cell may determine the position of the E-PHICH, it may avoidinter-cell interference through downlink scheduling excluding thefrequency band. In addition, a plurality of E-PHICHs mapped to aspecific RB may be multiplexed such that orthogonality is maintainedamong the E-PHICHs. The same orthogonalization method as used for CRS,CSI-RS, DM-RS, SRS, and PUCCH may apply to the E-PHICHs.

Embodiment 3

A method for operating a UE based on the above-described technicalfeatures according to a third embodiment of the present invention willbe described.

The operation of a UE is characterized mainly in that the UE acquires aUL grant and a DL grant from an E-PDCCH. This implies that a differentprocedure from a conventional UE operation procedure is required.

It is assumed that the E-PDCCH is precoded with a PDSCH and thus aspecific beam is formed. Hence, information of a PCFICH or an E-PCFICHmay be used to appropriately demodulate the E-PDCCH. The PCFICH and theE-PCFICH may provide resource allocation information about an E-PHICH.

The proposed E-PDCCH may be used in combination with the E-PCFICH or theE-PHICH or with the conventional PCFICH or PHICH. Many operationprocedures may be defined according to how the E-PDCCH is combined withother channels.

FIG. 13 illustrates an example of transmitting an E-PDCCH according toan embodiment of the present invention.

Referring to FIG. 13, an E-PCFICH and an E-PDCCH are applied. An LTE-AUE acquires resource position information about the E-PDCCH andinformation about the starting symbol position of a PDSCH bydemodulating the E-PCFICH. The UE also acquires HARQ ACK/NACKinformation from a PHICH.

Subsequently, the UE acquires a UL grant and a DL grant by decoding theE-PDCCH from a part of a PDSCH region, not the conventional PDCCHregion. As described before, the conventional PCFICH may be used toindicate transmission of an E-PDCCH only.

A PDSCH may be demodulated and decoded using information about thestarting symbol position of the PDSCH acquired from the E-PCFICH and theDL grant acquired from the E-PDCCH.

If the E-PDCCH is located at a fixed symbol position, it is possible todecode the E-PDCCH at the position. The symbol position of the E-PDCCHmay be changed by RRC signaling.

The PDSCH is demodulated using decoded vales of allocated resourcesbased on the decoding result of the E-PDCCH. The starting position ofthe PDSCH may depend on a CFI value. Preferably, the starting symbol ofthe E-PDCCH is preset to a specific symbol. However, the starting symbolposition of the PDSCH may be changed by RRC signaling.

FIG. 14 illustrates exemplary transmission of an E-PDCCH and an E-PHICHaccording to an embodiment of the present invention. Compared to FIG.13, it is noted that an E-PHICH is transmitted along with an E-PDCCH ina data region carrying the conventional PDSCH, unlike a general PHICH.

Referring to FIG. 14, if an E-PHICH is transmitted in addition to anE-PCFICH and an E-PDCCH, a UE may recognize use of the E-PHICH bydecoding the E-PCFICH. Information about resource positions and anorthogonal code of the E-PHICH may be acquired in the manner describedin the second embodiment of the present invention.

As described before, the introduction of an E-PCFICH, an E-PHICH, and anE-PDCCH according to the present invention can minimize interferencewith neighbor cells. However, the introduction of the E-PCFICH makes itdifficult to service legacy UEs in a corresponding subframe. In thiscase, a subframe supporting a legacy UE and a subframe dedicated to anLTE-A UE may be used separately. In order to minimize influence onlegacy UEs, a subframe carrying an E-PCFICH may be configured as anMBSFN subframe.

Embodiment 4

Even though a PDSCH and an E-PDCCH are located at fixed positions, thefixed starting positions of the PDSCH and the E-PDCCH may be differentaccording to the number of CRSs and a channel configuration.

For example, if a control region is configured to include only 2Tx CRSsand a PCFICH, the remaining region except for the first symbol isavailable to a PDSCH and an E-PDCCH. In this case, the fixed startingposition of the PDSCH and E-PDCCH is the second symbol.

Likewise, in case of 4 Tx antennas, 4Tx CRSs are located even in thesecond symbol. Thus, the fixed starting position of the PDSCH andE-PDCCH is the third symbol. If an MBSFN subframe is used, the fixedstarting position of the PDSCH and E-PDCCH may be different.

This means that the fixed starting position of the PDSCH and E-PDCCH isautomatically determined without additional signaling according to anantenna configuration and a used channel.

FIG. 15 is a block diagram of a communication apparatus according to anembodiment of the present invention.

Referring to FIG. 15, a communication apparatus 1500 includes aprocessor 1510, a memory 1520, an RF module 1530, a display module 1540,and a User Interface (UI) module 1550.

The communication device 1500 is shown as having the configurationillustrated in FIG. 15, for clarity of description. Some modules may beadded to or omitted from the communication apparatus 1500. In addition,a module of the communication apparatus 1500 may be divided into moremodules. The processor 1510 is configured to perform operationsaccording to the embodiments of the present invention described beforewith reference to the drawings. Specifically, for detailed operations ofthe processor 1510, the descriptions of FIGS. 1 to 14 may be referredto.

The memory 1520 is connected to the processor 1510 and stores anOperating System (OS), applications, program codes, data, etc. The RFmodule 1530, which is connected to the processor 1510, upconverts abaseband signal to an RF signal or downconverts an RF signal to abaseband signal. For this purpose, the RF module 1530 performsdigital-to-analog conversion, amplification, filtering, and frequencyupconversion or performs these processes reversely. The display module1540 is connected to the processor 1510 and displays various types ofinformation. The display module 1540 may be configured as, not limitedto, a known component such as a Liquid Crystal Display (LCD), a LightEmitting Diode (LED) display, and an Organic Light Emitting Diode (OLED)display. The UI module 1550 is connected to the processor 1510 and maybe configured with a combination of known user interfaces such as akeypad, a touch screen, etc.

The embodiments of the present invention described above arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim by asubsequent amendment after the application is filed.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware configuration, an embodiment of the presentinvention may be achieved by one or more ASICs (application specificintegrated circuits), DSPs (digital signal processors), DSDPs (digitalsignal processing devices), PLDs (programmable logic devices), FPGAs(field programmable gate arrays), processors, controllers,microcontrollers, microprocessors, etc.

In a firmware or software configuration, an embodiment of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. Software code may be stored in a memory unit and executedby a processor. The memory unit is located at the interior or exteriorof the processor and may transmit and receive data to and from theprocessor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

While the foregoing method and apparatus for transmitting and receivingdownlink control information in a wireless communication system havebeen described in the context of a 3GPP LTE system, by way of example,they are also applicable to various other wireless communicationsystems.

1. A method for receiving a downlink signal in a specific subframe froma base station at a user equipment in a wireless communication system,the method comprising: receiving a first control channel indicatingposition information about resources allocated to a second controlchannel; receiving the second control channel based on a control formatindicator included in the first control channel; and acquiring at leastone of a downlink grant and an uplink grant from the second controlchannel, wherein the second control channel is allocated to resourcesincluded in a data region of the specific subframe.
 2. The methodaccording to claim 1, wherein the control format indicator in the firstcontrol channel indicates the index of a starting symbol of the secondcontrol channel.
 3. The method according to claim 1, wherein the controlformat indicator in the first control channel indicates the index of anending symbol of the second control channel.
 4. The method according toclaim 1, wherein the control format indicator in the first controlchannel indicates the indexes of starting and ending symbols of thesecond control channel.
 5. The method according to claim 1, wherein thesecond control channel is precoded together with a data channel based ona reference signal.
 6. The method according to claim 1, furthercomprising receiving a third control channel indicating whether thesecond control channel is transmitted.
 7. The method according to claim6, wherein the third control channel is a Physical Control FormatIndicator Channel (PCFICH) and whether the second control channel istransmitted is indicated by a specific state indicated by a controlformat indicator of the PCFICH.
 8. A user equipment in a wirelesscommunication system, the user equipment comprising: a reception modulefor receiving a downlink signal in a specific subframe from a basestation; and a processor for processing the downlink signal, wherein thereception module receives a first control channel indicating positioninformation about resources allocated to a second control channel andreceives the second control channel based on a control format indicatorincluded in the first control channel, and the controller acquires atleast one of a downlink grant and an uplink grant from the secondcontrol channel, and wherein the second control channel is allocated toresources included in a data region of the specific subframe.
 9. Theuser equipment according to claim 8, wherein the control formatindicator in the first control channel indicates the index of a startingsymbol of the second control channel.
 10. The user equipment accordingto claim 8, wherein the control format indicator in the first controlchannel indicates the index of an ending symbol of the second controlchannel.
 11. The user equipment according to claim 8, wherein thecontrol format indicator in the first control channel indicates theindexes of starting and ending symbols of the second control channel.12. The user equipment according to claim 8, wherein the second controlchannel is precoded together with a data channel based on a referencesignal.
 13. The user equipment according to claim 8, wherein thereception module receives a third control channel indicating whether thesecond control channel is transmitted.
 14. The user equipment accordingto claim 13, wherein the third control channel is a Physical ControlFormat Indicator Channel (PCFICH) and whether the second control channelis transmitted is indicated by a specific state indicated by a controlformat indicator of the PCFICH.